Suspension system for sonic well drill or the like



A. G. BOBINE, JR 2,903,242

Sept. 8, 1959 SUSPENSION SYSTEM FOR SONIC WELL DRILL OR THE LIKE w n n m3 Sheets-Sheet 1 A rrok/vfx Sept. 8, 1959 SUSPENSIN SYSTEM FOR SONICWELL DRILL OR THE LIKE Filed Sept. 21, 1956 A. G. BODINE, JR

5 Sheets-Sheet 2 1N VEN TOR. ,4 55@ 7 50am/5, Je.

Sept. 8, 1959 A. G. BOBINE, JR 2,903,242

SUSPENSION SYSTEM EOE SONIC WELL DRILL OR THE LIKE Filed Sept. 21. 195e3 Sheets-Sheet 5 INVENTOR. E AQ 3f/2 7' G. 50a/M5, Je.

United States Patent O SUSPENSION SYSTEM FOR SONIC WELL DRILL R THE LIKEAlbert G. nadine, Jr., van Nuys, Calif.

Application September 21, 1956, Serial No. 611,131

1s claims. (cuss-2s) This invention relates to suspension systems forsonic vibratory devices in general, and, in an illustrative application,to a suspension system for a sonic well drill.

The principally known sonic drill of the class here referred to,disclosed and claimed in my patent No. 2,554,005V (sometimes known as ahalf, or full, wavelength drill, though it can be any multiple of halfwavelengths), comprises an elastic column such as a section of heavysteel drill collar suspended from a conventional ldrill string, thecollar being coupled at its lower end to a drill bit, and a longitudinalsonic standing wave being maintained in this collar by a suitablemechanical oscillator coupled thereto. This standing wave is a free-freepattern whereby velocity anti-nodes occur at both ends thereof. Thevelocity anti-node condition at the lower end is useful in thatvibration at this point is required in order to vibrate the bit. Thevelocity antinode at the upper end, however, in absence ofcountermeasures, undesirably sends sonic waves up the drill string. Suchleakage of sonic waves up the drill string representsV a serious loss ofsonic energy, and vibration of the drill string is in any event highlyundesirable for obvious reasons.

The sonic drill assembly may comprise an elastic vibratory column madeup of from one to several hundred feet of drill collar, in addition tothe bit, oscillator, and oscillator drive. It is accordingly very heavy,and the means by which this assembly is suspended from the drill stringmust be robust, as well as having the necessary compliance so that norestraint against vibration of the sonic drill is imposed thereby. Aprime requisite is that this suspension means must be of such nature aswill eiectively isolate the vibratory drill assembly from the drillstring, since, as stated above, transmission of sonic energy up thedrill string represents a serious power loss, shakes the derrick, and isgenerally undesirable. The suspension means must also, of course, bevery fatigue resistant. Still further, in a rotary drilling system, thesuspension means must be capable of transmitting torque, and it musthave provision for conducting a stream of drilling fluid. Moreover, itusually must be of such design that it can accommodate variable loadingof the drill collar by either pushing or pulling on the drill string.

A general object of the present invention is the provision of animproved sonic drilling system wherein vibrations are prevented fromtransmission from the vibratory drilling assembly to and up thesupporting drill string.

A further object is the provision of a mode of suspension of a sonicdrill from a drill string involving coupling to a velocity node, orstress anti-node, of the vibratory assembly.

A stilll further object is .the provision of a sonic drill wherein theupper end region of the vibratory assembly is the location of a stressanti-node, to which the drill string is directly coupled.

A further object is the provision of a suspension means for a half orfull wave type -of sonic drill assembly,

to be interposed between the drill assembly and the drill string,characterized by effective isolation of the vibratory drill assemblyfrom the drill string.

A further object is the provision of a suspension means as defined inthe preceding object, having such a degree of dynamic compliance thatsubstantially no restraint to vibration is imposed thereby upon thesonic drilling assembly.

A still further object is a suspension system having low damping.

A still further object is the provision of a suspension means which isfatigue proof over long periods of service.

A still further object is the provision of a suspension system for ahalf or full wave sonic drill, designed also for effective transmittalof torque, for conduction of drilling iluid, and for accommodation ofimposition of load by the drill string, or reduction of load by exertingtension in the drill string.

Further objects of the invention are the provision of correspondingimprovements in suspension systems for other vibratory systems wherecorresponding or analogous conditions and problems are encountered andmust be met.y

Generally stated, the present invention contemplates coupling of thesupporting drill string directly to `a velocity node (stress anti-node)i.e., a region of high mechanical impedance, of the elasticallyvibratory system of the sonic drill. The concept of mechanical impedancewill be understood to signify, in a mechanical, elastically vibratingsystem, the ratio of cyclic peak force acting at any given point in thesystem to Vdisplacement velocity at that point in the system. It will beseen that a region of high mechanical impedance is one at which cyclicforce amplitude is maximized, but displacement velocity, and thereforealso vibration amplitude, is minimized, or reduced substantially tozero. It will be seen that coupling of the drill string directly to` astress anti-node of the sonic drill, in accordance with the invention,is in direct contrast to some prior sonic drilling systems of the halfwave type, wherein the upper end portion of the vibratory system is thelocation of a velocity anti-node, and the drill string has been coupleddirectly thereto, with consequent maximum vibration transmission intoand up the drill string. It may be noted in passing that efforts havebeen made to introduce vibration insulators between the vibratory upperend portion of a half wave or full wave type sonic drill and the drillstring, but that, as experience has demonstrated, such attempts, becauseof the high power involved, have met with great difficulty. Gooddrilling rates have been attained, but relatively severe vibration ofthe drill string has not been prevented when drilling at high power.

Referring now particularly to the half or full wave type of sonic drill,broadly considered, the invention contemplates, as stated above, thecoupling of the drill string directly to a velocity node, or in otherwords, to a stress anti-node, of the vibratory system. It will berecalled that a half or full wave sonic drill has velocity anti-nodes(regions of maximum vibration amplitude) at the upper and lower ends ofits elastic vibratory column (from which circumstance such a column isdescribed acoustically as a free-free bar or column), and that the rstvelocity node, or stress anti-node, is spaced a quarter wavelengthdistance down from the upper end. Accordingly, in one form of theinvention, the drill string is attached to the vibratory assembly atsuch stress antinode region, located a quarter wavelength distance downfrom the upper end of the vibratory column.

In one preferred form of the invention, applicable to the half or fullwave type of sonic drill, there is provided, in addition to thevibratory elastic column, a vibration lisolator comprising a discreteacoustic circuit having a region of high mechanical impedance, whereatit is attached to the drill string, and having also a region of lowmechanical impedance, whereat it is coupled to a low impedance region ofthe elastic column of the sonic drilling assembly. By use of asuspension system hc ving high impedance at its drill string attachmentpoint, there results minimal acoustic coupling to the drill stringabove; and by the provision of a suspension system having low impedanceat its point of connection to a low impedance region of the sonic drillassembly, there is offered minimal blocking impedance to the sonicdrill.

Mechanical impedance is, of course, the vector resultant of resistiveand reactive components. The resistive component can be made low byproviding for low damping. The reactive component at the point ofcoupling to the drill can be made low by tuning the suspension system toresonance at the frequency of operation of the drill, eitherfundamental, or harmonic, depending upon which is to be combatted. Thismay be done by a suitable choice of mass and 'compliance within thesuspension, e.g., in a lumped constant system, by such a relationship ofmass to elastic compliance that the system is selectively frequencyresponsive, or resonant at the operating frequency of the drill. It mayalso be accomplished by use of a distributed constant system having suchmass, elasticity, and distribution of both mass and elasticity as toprovide a resonant standing wave system that is frequency responsive tothe operating frequency of the drill. Such a system has both velocityanti-node and pressure anti-node regions, the former a region of lowimpedance, affording a suitable coupling point for the drill, and thelatter a region of high impedance which affords a suitable couplingpoint for the drill string.

One physical example of the last mentioned type of suspension system,having such acoustic properties, comprises a heavy mass directly coupledto the drill string, and a slender tubing of quarter wavelength for thefundamental resonant operating frequency, or harmonic of interest, ofthe sonic drill assembly, connecting such mass to the upper end of thesonic drill assembly, as set forth above. As another example, there maybe used, in lieu of the heavy mass, another quarter wavelength ofcompliant tubing, connected to the first quarter wavelength tubingadjacent the coupling point to the drill string. The performance of suchdevices will be more fully set forth in the ensuing detaileddescription. A number of additional configurations are within the scopeof the invention, and some of these will be described hereinafter.

Another form of the present invention involves a modiiication in theconfiguration of the sonic drill which facilitates direct coupling ofthe drill string to `the stress antinode region of the drill, this formof sonic drill having been first disclosed in my prior application Ser.No. 442,805, filed July 12, 1954, entitled Polyphase Sonie Earth BoringDrill and Process, of which the present application is acontinuation-in-part. 'Ihis configuration results from the folding of ahalf wave sonic drill into a double (or plural) legged elastic barstructure, the midpoint of which is uppermost, with the legs, of quarterwavelength, depending therefrom. The resulting structure may form aninverted U or a depending fork, or two concentric legs joined at thetop. The now uppermost midpoint of the structure remains the location ofa stress anti-node, or velocity node, after the described foldingf Inaccordance with the present invention, the drill stem is then directlycoupled to this non-vibratory uppermost midpoint of the plural legstructure. Analyzed acoustically, I have provided a plurality of coupledacoustic support elements (acoustic elastically vibratory bars)operating with a balanced phase difference and joined at respective highimpedance regions to achieve a non-vibratory support point, which istherefore incapable of transmitting Vibrational energy into any meanscoupled thereto; and

I have directly coupled the suspension drill string to thisnon-vibratory support point.

Referring now to the drawings showing certain selected illustrativeembodiments of the invention:

Fig. 1 is an elevational view of a typical half wave sonic drillassembly showing a fragmentary lower end portion of a suspension meansin accordance with the invention;

Fig. 2 is a view partly in elevation and partly in section, withlongitudinal portions of the sonic drill assembly broken away, showingone illustrative suspension means according to the invention, coupled toa sonic drill of the type represented in Fig. l;

Figs. 3, 4, 5 and 6 are views similar to Fig. 2, but showingmodifications;

Fig. 5a shows a modification of a portion of Fig. 5;

Fig. 7 is a View, partly in elevation and partly in section, showing alumped constant type of suspension means for a sonic drill.

Fig. S is an elevational view, partly in section, showing anotherembodiment of the invention;

Fig. 9 is a longitudinal medial section of the embodiment of Fig. 8,extending downwardly to a point just below the head of the forkstructure;

Fig. 10 is a longitudinal medial section of the lower end portion of theembodiment of Fig. 8;

Fig. 1l is a section taken on line 11-11 of Fig. l0;

Fig. 12 is a bottom elevational view of the embodiment of Fig. 8;

Fig. 13 is a section taken on line 13-13 of Fig. 10;

Fig. 14 is a section taken on line 14-14 of Fig. 1l; and

Fig. l5 is a section taken on line 15-15 of Fig. 11.

Referring first to Fig. 1, numeral 10 designates generally a typicalhalf wave sonic drill assembly, comprising, in this instance, an elasticcolumn rod or bar, made up of three more or less conventional drillcollars 11, connected to one another by conventional drill collarcouplings 12, a bit 13 coupled to the lower-most drill collar 11, and anoscillator and driver or power means therefor, represented at 14,coupled to the uppermost drill collar. The unit 14 may comprise amechanical vibrator in the form of a plurality of rotating eccentricweights, so arranged that while longitudinal components of vibration areadditive, lateral components of vibration are cancelled, powered by aturbine which is in turn driven by the usual stream of mud fluidcirculated down through the drill string as in conventional rotarydrilling practice. Suitable forms of such devices are described in myaforementioned Patent No. 2,554,005.

Referring now also to Fig. 2, a fragmentary lower end portion of thedrill string is indicated at 16, and between this drill string and thesonic drill is intercoupled the suspension system or isolator I of theinvention. This isolator includes a massive bar 18, conventionallycoupled, as indicated at 18a, to the lower end of the drill string. Thisbar 18 has circulation bore 19 for drilling iiuid. In a typicalembodiment, the bar 18 may be of a length of, for example, 40 feet, anoutside diameter of eight inches, and may comprise a section ofconventional drill collar. The isolator further includes a relativelyslender pipe 20, of a typical length of approximately 70 to 75 feet, andwhich may comprise two intercoupled sections of conventional drill pipe,coupled at its upper end to the lower end of bar 18, and at its lowerend to oscillator and power unit 14, all as clearly indicated in Fig. 2.Assuming the sonic drill assembly 10 to vibrate in its fundamental halfwavelength standing wave mode, and to have an over-all length of feet,it will be seen that the slender pipe section 20 is of quarterwavelength (or slightly more, in view of the fact that the mass of bar18 is not infinite) for the fundamental resonant frequency of operationof the drill. It is, in other words, frequency responsive to the drill.

In operation and still assuming the sonic drilling assembly 10 tovibrate in a half-wavelength mode, the slender, elastically compliantpipe section 20 then vibrates at the same frequency in a, v`quarterwavelength 139996, its UPPer end standing substantially stationary inview of its being anchored to the massive bar 18, and its lower endvibrating vertically in consonance with the vertical vibration of theupper end portion of the sonic drilling assembly 10. The intercoupledlower end portion of pipe 20 and upper end portion of drilling assemblywill be seen to be at a velocity anti-node of the vibratory system, andthe intercoupled upper end portion of pipe and massive bar 18 fto be atwhat is eii'ectively a velocity node, or stress anti-node, of thesystem. The massive bar 18 will further be seen to be a region of thesystem characterized by high mechanical impedance, and the point ofinterconnection between the lower `end of pipe 20 and sonic drillingassembly 10 to be a region of low mechanical impedance of the system.

Under the conditions as stated, bar 18 remains firm and steady, and doesnot transmit material vibratory energy up the drill string 16.V The pipe20, however, is a relatively compliant member for the criticalfrequency, and its lowerend portion vibrates naturally in consonancewith the vibration of the upper end portion of the sonic drillingassembly, so that the vibration of the latter is unimpeded. It vwill beobserved that by having given the pipe 20 effectively a quarterwavelength for the natural resonant :frequency of vibration of the sonicdrilling assembly, it has been pre-tuned, in combination with mass 18,to vibrate resonantly at the fundamental frequency of operation of thesonic drilling assembly. It accordingly participates in the wave actiongenerated in the sonic drilling assembly without presentation ofmaterial blocking impedance. It will further be observed that the bar 18and compliant pipe section 20 are adapted equally for imposingcompressional loading on the sonic drilling asseml bly, or for exertingItension thereon, thus not interfering with controlled application ofbias loading on the sonic drill. It will further be evident that thesystem is one of low damping, and therefore of low energy dissipation.

As described in the immediately preceding passages, the suspensionsystem has been tuned to respond to the fundamental resonant frequencyof the sonic drill. However, the sonic drill may have important andsometimes troublesome overtone frequencies, and it will be evident thatthe suspension system, or isolator, may alternately be designed torespond critically to these. Such overtone frequencies may be initiallyinduced, or may be stimulated and/ or augmented by striking of the bitagainst the rock. For example, assuming that it is .the second harmonicof the sonic drill that is to be combatted, the isolator device, insteadof being a one-quarter wavelength device for the fundamental frequencyof the sonic drill, is made to be a quarter wavelength device for thesecond harmonic of the sonic drill. In other words, the length of `itselastic column for this case is halved. Also, I may use tWo of thesuspension systems in tandem, one dimensioned for critical response tothe fundamental, and the other for critical response to the harmonic.

As mentioned above, the sonic drill may be designed for full wavelengthvibration, in which case the elastic column, or drill collar, has avelocity anti-node at each end, and another velocity anti-node at itsmidpoint. If the operating frequency remains 4the same as for the halfwave case, the length of the drill collar is doubled, and

Vbecomes 280 feet. The length dimension for the isolator,

however, remains the same, since the length of a quarter wave along thesystem has not been altered. The same result would follow for a sonicdrill having a collar length of one and one-half wavelengths. It mightbe here mentioned that for increasing the weight on the bit a fullwavelength sonic drill is desirable and quite feasible, as is a systemof one and one-half wavelengths; and that for these cases, it isadvantageous to maintain the frequency by operating at fthe higherharmonic, so as to be thus able to increase the over-all length of thesystem without lowering the operating frequency. It is also to bepointed out that when operating a sonic drill at a fre- 6 quency to giveone full wavelength performance, for example, a half wavelength mode, aswell as higher har monics (second harmonic and above) may be set uptherein by reason of impacting against the formation. Isolators properlydimensioned for response to any or all such frequencies may obviously beused in the system.

It will be seen that for each example given above, the isolator isdimensioned for quarter wavelength performance at the critical frequencyof the component of vibration of the drill that is to be combatted. Interms of impedance, it has a low impedance where connected to the drill,and a high impedance where connected to the drill string. It shouldfurther be understood that these impedance characteristics areself-contained characteristics in the isolator, at the criticalfrequency for which it is dimensioned, and are not contributed to byeither the sonic drill or the drill string. The requisite is that theimpedance of the isolator where connected to the sonic drill below,i.e., comparable to the low impedance of the sonic drill at theconnection point, so as to present minimal blocking impedance to thedrill; and that the impedance be high at the point of connection to thedrill string, `so as to have minimal vibratory motion at that connectionpoint, and therefore minimal acoustic or vibratory coupling to the drillstring.

Fig. 3 shows a modied isolator I1, .the same type of sonic drill againbeing designated by numeral 10, and comprising a column of drill collars-11 and bit 13, and oscillator and driver L114. At the top of the ligureis fragmentarily illustrated the lower end portion of a massive bar 30,formed with circulation bore 31, and this bar, like bar 18 of Fig. 2,may comprise a section of conventional drill collar of a typical lengthof 40 feet, it being further understood that the upper end of collar 30is coupled in conventional manner to the drill string above, not shownin Fig. 3, but understood to be arranged in a manner similar to thatshown in Fig. 2.

Screw-threaded onto the lower end of collar 30 isa long suspensionsleeve 32, whose lower end is furnished with an internal screw-threadedcoupling to the lower end of a relatively slender upstanding pipe column33 reaching nearly to the lower end of collar 30. This pipe column 33may conveniently comprise two intercoupled lengths of conventional drillpipe, as illustrated, suitable annular Working clearance being providedbetween pipe 33 and sleeve 32. A slender pipe column y34, equivalent inlength and cross section to the pipe 33, is coupled to the lower end ofpipe 33 below the lower extremity of sleeve 32, and its lower end iscoupled to oscillator and power unit 14 of the sonic drill, lasindicated. This pipe 34 may also be composed of two lengths ofconventional drill pipe, the lower end of the lower length being adaptedfor coupling into the larger diameter unit 14.

Assuming the sonic drill assembly 10 again to vibrate in a halfwavelength standing wave mode, i.e., as a freefree bar, and to have anover-all length of feet, pipe sections 33 and 34 each may have a lengthof approximately 70 feet, and each is accordingly of quarter wavelengthfor the fundamental resonant frequency of operation of the drill. Inother words, pipe sections 33 and 34 taken `together comprise a halfwave system, being effectively what is known in acoustics as a free-freebar, whereby the whole vibrating system is one full wavelength.

In operation, with sonic drilling assembly 10 vibrating in its halfWavelength mode, the elastic suspension column made up of pipe sections33 and 34 vibrates also, at the same frequency, in a half wavelengthmode, its lower end vibrating in 'consonance with the vertical Vibrationof the upper end portion of the sonic drilling assembly 10, its upperend vibrating equally and oppositely thereto, and its center section,where the two pipe sections 33 and 34 are intercoupled to one another,and to the lower end of suspension sleeve 32, standing substantiallystationary. The two pipe sections 33 and 34 .thus

are dynamically opposed to one another during this vibratory operation.The intercoupled lower end portion of pipe section 34 and the upper endportion of drilling assembly 10 are then at a velocity anti-node of theoverall vibratory system, the upper end portion of pipe 33 is at anothervelocity anti-node of the system, and the intercoupled lower end portionof pipe 33 and upper end portion of pipe 34 are at a velocity node ofthe system. Each velocity anti-node will be at a low impedance region ofthe vibratory system, and the intercoupled end portions of pipes 33 and34 are at a region of high mechanical impedance of the system. Sleeve 32is somewhat ilexible and elastic, and of substantially quarterwavelength (or slightly longer in view of the fact that the mass 30 `isnot infinite) for the fundamental resonant frequency of the system.Accordingly, any small remaining Vibration in the high impedance regionwhere the pipes 33 and 34 are coupled to one another, sets up a smallcorresponding quarter wave molde of vibration in the sleeve 32. Themassive collar 3i) coupled to the upper end portion of sleeve 32establishes a very high mechanical impedance at that point of coupling,such that while sleeve 32 may vibrate slightly in a quarter wavelengthmode owing to any remaining vibration at the juncture of pipes 33 and34, the coupling point between collar 30 and sleeve 32 functions as ahighly rigid anchorage, and transmission of any vibratory energy up thecollar 30 is reduced to negligible amplitude. The isolator, consideredas a unit apart from the remainder of the system, will be seen to have apoint of low impedance for the critical vibration frequency where it isto be connected to the sonic drill, i.e., of magnitude comparable to thelow order of impedance magnitude at the top end of the drill, and a highimpedance region at its midpoint, where the pipe column 33, 34 is hungfrom the sleeve 32. The sleeve 32, in turn, has a relatively lowimpedance where connected to the column 33, 34, such that any smallvibration at this junction point can be transmitted to the sleeve. Themass 30 at the top, however, is of very high impedance, and holds theupper end of sleeve 32 rigid, such that a small amplitude quarter wavetype vibration can occur in the sleeve, but is blocked from upwardtransmission by the mass 30j. As with the system of Fig, 2, the systemof Fig. 3 may also be adapted for critical response to a harmoniccomponent of standing wave vibration present in the overall wave patternof the sonic drill. To design it for critical response to the firstovertone, for example, the length of the pipes 33 and 34 and of thesleeve 32 are simply halved. The discussion given above of the variousmodes of vibration that can occur in the sonic drill, and thedimensioning of the isolator for critical response thereto, applies herein similar manner.

Fig. 4 shows another embodiment of suspension means orisolator I2 inaccordance with the invention, the `sonic drill, of the same type as inthe preceding figures, being again ydesignated by numeral l0, and beingmade up of components as before, bearing the same reference numerals.Coupled to the upper end of oscillator and driver unit 14 for the sonicdrill is the lower end of a long, heavy section, elastic pipe member 40,whose length, assuming it to be designed for critical response to the`fundamental resonant frequency of the sonic drill, and

assuming the drill to be driven in its half wave mode, is substantiallyequal to the length of the sonic drill assembly 10. This pipe 40 is hereshown to be of the same outside diameter as the drill collars l1. At itsmidpoint, the pipe 40 has an internally reduced `and internallyscrew-threaded section 4l, into which is coupled the screw-threadedcoupling pin on the lower extremity of elongated drill pipe 42, suitableannular clearance being provided between pipe 42 and the bore of pipe40, as illustrated.

In operation, pipe 40 vibrates in a half wave mode, in a manner similaito the intercoupled pipesections 33 and 34 of the embodiment describedimmediately above. That is to say, the lower end portion of pipe 40vibrates in consonance with the upper end portion of the sonic drill,the upper end portion of pipe 40 vibrates in opposition to the lower endportion of said pipe, and the intermediate section of pipe 40 standssubstantially stationary. In acoustic terms, the lower and upper endportions of pipe 40 are low impedance, velocity anti-node regions, whilethe intermediate section of the pipe is a high impedance, velocity noderegion of the system. The high impedance intermediate section of pipe 40thus standing substantially stationary, vibrations in the sonic drillassembly and in the upper and lower regions of the pipe 40 are isolatedfrom the drill pipe 42. The fuller theoretical discussion given inconnection with the earlier described embodiments applies here as Well.

With further reference to Fig. 4, the isolator I2 shown therein has beenproperly described in the foregoing as a device interposed between theupper end of the elastic collar column of a half wave sonic drill andthe lower end of a drill string. It is also correct, however, to Viewthe interposed isolator device as a halfwave length upward extension ofthe elastic drill collar or column of the sonic drill, thus convertingthe elastic column of a half-wave sonic drill, for example, to fullwavelength, with provision being made for direct coupling of thedrilling string to the stress anti-node region at the mid-point of 'thesaid half wavelength extension. The device I2 may, indeed, be readilyfabricated from two drill collars, connected by a double-pin sub, towhich sub the drill string is coupled by a suitable threaded joint. Inshort, the embodiment of Fig. 4 may be regarded, broadly, as made up ofa free-free vibratory elastic column, with a.V drill string suspensioncoupling attached directly to an intermediate high impedance or stressanti-node region of the column. Moreover, the column length may be equalto any number of half wavelengths, including unity.

Fig. 5 shows another embodiment, used again with a sonic drill comprisedof drill collars 11, bit 13, and oscillator or power unit 14. Thesuspension system in this case contains components similar to those ofthe system of Fig. 2, including drill collar 18' suspended from drillpipe 16', and slender pipe 20' coupling the lower end of collar 18 tothe upper end of the sonic drill. The lengths of the members may also beas in Fig. 2. That is to say, pipe 20' is of quarter wavelength for theresonant frequency of interest of the sonic drill. The embodiment ofFig. 5 differs from that of Fig. 2 in that an elastic sleeve 4Ssurrounds the pipe 20', its upper end being rmly joined, as by asuitable screw-threaded coupling, to the upper end of pipe 20. Thesleeve 45 is of substantially the same length as the pipe 20', so thatit also is of quarter wavelength for the frequency of interest of thesonic drill.

Considering the operation of the embodiment of Fig. 5 irst without thesleeve 45, it will be recalled from a discussion of Fig. 2 that theupper end portion of the elastic coupling pipe 20 is at a velocity nodeof the system, and is a region of relatively high impedance, thiscondition depending upon the heavy mass afforded by the collar 18. Thecollar 18 provides a substantial blocking impedance for the vibratoryenergy otherwise traveling up the system. Considering now the pipe 45,this added component furnishes a dynamic means for balancing thevibratory standing wave action the pipe 20', and may be used eithertogether with massive collar 1S', for additional stability andisolation, or as an alternative therefor. Accordingly, considering thesystem in absence of the heavy mass afforded by the collar 18', it isfound that the quarter wavelength elastic sleeve 45, extendingdownwardly around the quarter wavelength pipe section 20', is set intoquarter wave standing wave action in phase opposition to the standingwave experienced by the pipe 2%. Thus, as pipe 20 elastically contracts,sleeve 45 elastically elongates, and vice versa. By designing the sleeve45 to have elasticity and mass distribution equivalent to that of pipe20', the upper end juncture of the two stands substantially stationary,and becomes a high impedance, velocity nodal region of a folded lwavelength standing wave system. The performance is analogous to thatobtained with the system of Fig. 4, with the exception that the twoquarter wavelength portions of the 'system of Fig. 5 comprised of thepipe 20' and sleeve 45, which are again in phase opposition, liealongside each other, such that longitudinal forces are again everywheredynamically balanced. The upper end juncture of pipe 20' with sleeve 45accordingly stands substantially stationary, and is a point to which thedrill pipe above might be vdirectly attached. It is deemed of furtheradvantage, however, to include the heavy drill collar 18 so as to havean additional inertial 'type of high impedance in the system, whichaffords additional assurance of substantially total isolation of thevibratory system from the drill stem.

Fig. 6 shows still another embodiment of the system, using again a sonicdrill 10 including oscillator or power unit 14, drill collars 11, andbit 13. In this case, as in Fig. 2, the drill pipe 16 is coupled at itslower end to a massive drill collar, here indicated at 50, and acompliant coupling 51 whose effective critical frequency is maderesponsive to the resonant frequency of interest of the sonic drill.

`For compactness, the coupling 51 is formed of three telescoped tubularelements, an outside tube 52 screwthreadedly attached at its upper endto the lower end of collar 50, an immediate tube 53 annularly spacedinside tube 52 and screw-threadedly connected at its lower end to thelower end of pipe 52, and an inside pipe 54, annularly spaced insideimmediate pipe 53, and screwthreadedly connected at its upper end to theupper end of pipe 53. The lower end of pipe 54 is coupled to the upperend of the sonic drill, as shown. The total effective length of thethree sections 52, 53 and 54, is made equivalent to a single, straightquarter wavelength pipe. Owing to the doubling back or folding of thecoupling, however, the total over-all length of the coupling for quarterwave operation analogous to that of Fig. 2 is generally found to besomewhat less than that of a straight pipe. This is a matter dependingsomewhat upon the masses of the coupling elements and the mechanicaldesign, which cause the system to behave somewhat as one having lumpedconstants, with resulting reduced length for the same resonantfrequency. Frequency response, however, is equally important.

The elastic coupling 51 behaves essentially as does the coupling pipe 20of Fig. 2. However, the inside pipe 54 and outside sleeve 52 are alwaysin tension, or compression, at the same time, whereas the intermediatemember 53 is in compression while members 54 and 52 are in tension, andis in tension while members 54 and 52 are in compression. The membersthus cooperatively elastically contract, or elongate, as the case maybe, to give a folded quarter wavelength performance which is theequivalent of that of Fig. 2. Of course, the amplitude of elasticelongation and/or contraction is a maximtun at the lower end portion ofthe inside pipe 54 and progressively diminishes to substantially zero atthe point of coupling of the outside pipe 52 with the collar 50.

It will be seen that in the system of Fig. 6, the circulation fluidpasses through the bore of collar S0, to be received by pipe 54 andthence conducted to the sonic drill.

Fig. 7 shows a lumpedf constant type of isolator suitable for afree-free sonic drill, and which is analogous in basic respects to thatof the standing wave systems ofthe first described embodiments. In thiscase, the lower end portion of a drill collar 60 (which may be similar,for eX- ample, to the drill collar 18 of Fig. 2, and may be similarlysuspended from the more slender drill pipe above) has been formed at itslower end with a threaded pin 61 which is screwed into the threaded box62 of a tool joint 63 integrally joined with the upper end of heavyhelical spring 65. Integral with the lower end of spring 65 is a tooljoint 66 having threaded pin 67 adapted to be screwed into a couplingbox at the upper end of a sonic drill such as represented in the earlierfigures of the drawings. The spring 65 is here shown to be furnishedwith a iluid pipe 70 whose upper extremity is received in a bore 71extending up into tool joint 63, an enlarged threaded bore 72 above bore7l receiving an annular ange 73 on the upper extremity of pipe 70, and athreaded retaining ring 74 being screwed into bore 72 to x `the pipe 70in assembly with the upper tool joint 63. The lower end portion of pipe7@ is slidably received within a bore 74' extending downwardly into tooljoint 66, suitable packing being used at '75, as clearly shown.

This helical spring isolator is designed with such mass land elasticityconstants as to have a natural resonant vibration frequency matched tothe vibration frequency of interest, fundamental or harmonic, of thesonic drill to which it is coupled. This is determined by the formula-in which m is equivalent mass, k is effective spring constant and f isthe frequency to be isolated. Such frequency response match having beenprovided, the spring elongates and contracts in consonance with thevertical vibration of the upper end of the sonic drill, the upper end ofthe spring, where connected to the massive collar 60, standingsubstantially stationary. Circulation lluid is conveyed through thespring by the pipe 70, previously described as Xedly mounted within thetool joint 63 at the Iupper end of the spring, and fitted for relativesliding movement within the lower Itool joint 66.

Reference is next directed to Figs. 8 to l5, showing an illustrativeplural legged quarter wavelength sonic drill with an uppermost commonhigh impedance stress antinode region, and direct coupling between thedrill string and such high impedance region. The illustrative drill,shown employs a leg structure comprising a center leg and .an outsidetubular leg depending from a unitary head. .This embodiment utilizes anunbalanced rotor type of .vibrato-r in one leg, in this instance, in thelower portion fragmentarily at 90. In most cases, the drill string i11-`cludes one or more standard drill collars a, coupled yto the upper endof member at box 101, giving added weight on bottom, and theconventional drill pipe is then coupled to the upper end of thesecollars. The lower end of the member 100 has a threaded box 102 intowhich is screwed the coupling pin 102a on the upper end of a cylindricalmember 103 forming the lower end portion of the outside leg structure.This member 103 has a central longitudinal slot 104 running nearly fromend to end, in which is received, with good clearance, a vibratorhousing 105, later described in more particular. The lower end portionof body 103 is tapered outwardly, as at 106, to furnish a tubular lowerextremity 107 of somewhat enlarged diameter, and inset in this lowerextremity are hardened bit elements as indicated typically at 108.

The vibrator mechanism inside housing is driven through a long verticaltransmission shaft 109 from a mud dxiven'turbine 110 housed in the upperend portion of tubular member 100. The bladed turbine stators 111 aresupported within the tubular member 100 by means of a shoulder formed at112., and the stators are separated by intervening spacers 113. Engagingthe upper stator 111 is a sleeve 114, held in place by a retainer 115screwed into box 101, and provided with radial vanes or ribs 1.16supporting a central distributor hub 117 shaped to guide the mud fluidfrom above downwardly to the turbine blades, as indicated. The turbineshaft 120 has near its upper extremity a tapered section 121 on which isytightly mounted a turbine rotor head 122, the latter having adownwardly extending sleeve portion 123 formed with an outwardlyextending ange 124 at its lower end. Mounted on sleeve 123 andsup-ported by the flange 124 are the bladed turbine rotors 125,separated by spacers 125. A cap 127 engages the top rotor and the partsare held in assembly by means of a nut 12S screwed down onto thethreaded upper extremity 129 of the turbine shaft. The blades of thestator and rotor of the turbine will be understood to be properlyinclined, in accordance with conventional practice in fluid driventurbines.

The section 1206i o-f the turbine shaft is furnished with suitablepacking, as indicated at 131), carried by a reduced tubular upwardextension 131 of a tubular bearing housing 132 annularly spaced insidethe tubular exterior member 100 by positioning lugs 132a formed on saidhousing, the extension 131 being received, with clearance, inside theturbine rotor sleeve 123, as indicated. The annular space 134 betweenthe bearing housing 132 and the outside tubeltlt) forms a channel forthe mud fluid discharged from the turbine. Below the section 120a theturbine shaft has a flange or collar 135 furnishing a shoulder whichengages a washer 136 supported by the inner race ring of the uppermostof a stack of roller bearings 137, the lowermost being retained by a nut138 threaded on the shaft. The outer race rings of these bearings arereceived in a bore in the housing 132, and supported therein by aretainer 139.

Threaded into the lower end of bearing housing 132 is the reduced neckof an oil housing 140, of the same diameter as bearing housing 132, themud uid channel 134 thus continuing down around the outside ofthehousing 140. The turbine shaft 12), whose lower end portion 120b reachesdown into oil housing 140, has a longitudinal bore 145 extendingdownwardly through its lower end from a point just below collar 135, andthis bore is tapered downwardly within the portion 120k of the shaft, asindicated at 146. The turbine shaft portion 12% is also tapereddownwardly, and its lower end is formed as a spur gear 147 meshing withinternal gear teeth 148 in a cup-like coupling member 149 tightlymounted on the upper end of transmission shaft 109. Oil ports 150 areprovided in the lower portion of cup 149.

Oil is maintained in housing 140 to such a level as indicated at L, andis supplied through ports 150 to the bottom end of the hollow turbineshaft. Y The aforementioned washer 136 is radially drilled, as at 151,and the turbine shaft is formed with drill holes 152 establishingcommunication between the interior of the hollow shaft and the drillholes in the washer. When the turbine shaft rotates, oil climbs in thetapered portions of the bore through centrifugal force, and fills thehollow turbine shaft up to the level of the drill holes 152. Oil isforced out through the drill holes 152, and thence out through the drillholes 151 in washer 136 to lubricate the bearings.

The lower end of oil housing 140 is anged and bolted, as indicated at154, to corresponding flange formations on the upper end of a long,generally cylindrical steel shank or -rod 155, which forms a portion ofthe head and center leg structure of the fork. The upper end portion155a of this shank or rod 155 has a long downward taper 156 and engagesa complementary taper 157 on the inside of tube G. The parts 155 and 100are pressed or driven together to produce a tight wedge iit, and thusbecome structurally integrated to one another in the region of thetapered joint. This region of said members comprises the high impedancehead structure 158 of the device. It is the location of a stressanti-node, or velocity node, during operation.

lust below the taper, the internal diameter of bore member is enlarged,as indicated at 159 (Figs. 8 and 9), to provide a crotc and an annularmud fluid channel 160 between the members 100 and 155. This channel 160receives mud uid from channel 134 via a suitable number of passages 161extending through the upper end portion a of the shank 155, as clearlyshown in Fig. 9. The channel is continued for a short distance down intomember' 103, as at 16041 (Fig. 10), where communication is had via ports161a with two longitudinal mud slots 162 formed in opposite sides of themember 103 (see also Fig. 14). The mud slots 162 are closed on theoutside by cover plates 16,3 welded in position, as indicated, anddischarge at their lower ends, via ports 164, into the space inside thelower tubular extremity 107 of member 163, from which final dischargetakes place at the bottom of the well hole. Y

The shank 155 has a central bore 166, extending downwardly from asimilar bore 167 through the bottom of oil housing 150 and these boresreceive bearing bushings 168 for transmission shaft 109, the bushingsbeing spaced by sleeves 169. A plug 170 screwed into the top of bore 167holds the bushings and spacers in assembly at the top, and hassufficient clearance with shaft 109 to pass oil from housing 141) downinto the space 171 around the shaft.

Press fitted on the lower end of shaft 109 (Fig. l0) is a drive sleeve172 having internal splines 173 meshing with splines 174 on vibratordrive shaft 175. The lower end of shank 155 is formed with an internallythreaded box 180 to receive a threaded pin 181 on a flanged head member182 at the upper end of the vibrator housing 105.

The vibrator housing is longitudinally split into two halves 105:1 andlliSb, bolt connected as at 183 (Figs. l0, ll and l5). The two housinghalves are formed with a plurality of mating shaft portions 184,surrounded by bushings 185, and journalled on these bushings areeccentrically weighted vibrator rotors 187. In the illustratedembodiment, there are four such rotors 187, all in vertical alinement,and interconnected by suitable gears. Each rotor is formed with a spurgear 188, and the spur gears of the two upper rotors are in mesh withone another, as are the spur gears of the two lower rotors. The lowergear of the upper pair is interconnected with the upper gear of thelower pair through an idler Vgear member 189. The gear on the upperrotor is driven from the vibrator drive shaft through a gear set 190.

The weights W of the unbalanced rotors are positioned so that all movevertically in unison, which is accomplished if for instance they are allinitially positioned with their weights at the bottom, as in Fig. l1.Ylt will be evident that each eccentrically weighted rotor will exert athrust at its bearing as it rotates. Only the thrust in the verticaldirection is, however, useful. By arranging the rotors in pairs ofoppositely rotating members, the vertical components of thrust areadditive, while the lateral components are cancelled. Also, by use ofthe idler 189, the two inside rotors turn in the same direction, and thetwo outside rotors also turn inthe same direction, thus achievingbalance against couples.

Vibrator shaft 175 is journalled in suitable bearings contained in abearing housing 196 received in a bore 197 formed in the upper end ofvibrator housing 105, the housing 196 having at the top a flange 198engaging the top end of housing 105. A packing retainer 199 has asimilar' flange 211i? engaging the flange 19E, and this rerainercontains a suitable packing 201 around the shaft 175 to prevent oil fromabove leaking down into the inside of the vibrator housing. A angedpacking retainer 202 is placed between the ange 2li@ and the aforemeationed head number 182 (Fig. 11), the parts being secured in assembly bymeans of screws 2415 passing down through head member 182 and lianges202, 2130 and 198 to engage 13 in threaded sockets in the two halves ofthe vibrator housing.

A flanged iitting 210 is secured to the lower endof housing 105, as byscrews 211, and has a threaded coupling pin 212 engaging the threadedbox 213 of an inside bit member 214, the latter being provided, in thisinstance with a hardened insert blade 215 extending transverisely acrossthe space inside the outside tubular part 107. The bit element 215 ishere shown as elevated somewhat above the outside bit elements 108,being designed to disintegrate large fragments of formation initiallybroken free by action of the outside bit elements 108. It will beevident, however, that the bit element 215 may alternatively be placedon a level with the elements 108, and no limitation to the illustratedarrangement is accordingly to be implied. Also the bit element 215 maybe omitted, leaving the outside bit to do the work on the formation, theinside leg then being less damped, and contributing greater fly-wheeleffect to the system as a whole.k Moreover, the drill can be arrangedwith a bit only on the inside leg, so that the outside leg functions asa counterbalancing vibrator, with minimum damping.

It will be seen that the drill of Figs. 8-15 formsra structure having acentral leg formed by the shank 155 and vibrator, and an outside legstructure comprised of the centrally slotted body 103 and the portion ofthe outside tubular member 100 below the juncture of the latter with theshank member A155. The region of the member 155 and the member 100wherein said members are integrated structurally to one another, in thisinstance by the long taper jointat 156, 157, forms the high impedance,stress anti-nodal head structure 15S of the device. The length of thelegs below the head structure, i.e., from the crotch 159 to their lowerextremities, has an essential relationship to the frequency at whichsaid legs will vibrate, as mentioned earlier. For an operating frequencyof 120 cycles per second, this leg length should be approximately 33feet.

Operation is as follows: the turbine is driven by mud fluid pumped downthe usual drill string, the mud fluid being eventually discharged to thebore hole at the bottom, and forming a fluid column rising to the groundsurface around the drill string, in the usual way. The turbine shaft 120drives the vibrator connected to the lower end of the central leg of thestructure through the connections previously described, causing thevibrator to create an alternating force in a vertical direction at afrequency dependent upon the speed at which the turbine is driven ibythe mud llow. This speed is governed'by the rate at which mud fluid ispumped through the drill string at the ground surface. The verticalalternating force developed by the vibrator is exerted on the lower endof the shank 155, which comprises the central leg of the structure. Whenthe turbine is driven at such speed that the vibrator frequencyapproaches or coincides with the resonant frequency of the device, theshank 155 vibrates in the vertical direction with substantial amplitude.This frequency for resonant operation is given by the ratio where S isthe speed of sound in the material of the structure and L is the lengthof the legs. Each of the legs is capable of elastic vibration in alongitudinal direction as a fixed-free bar of quarter wavelength, or oddmultiple thereof, assuming it to be acted upon by an alternating forceof resonant frequency. Such resonant elastic vibration is set up in thecentral leg by direct drive from the vibrator when operated at theresonant frequency. A velocity anti-node then exists at the lower end ofthe central leg, and va high impedance estress anti-node exists at itsupper end, at the head or upper end juncture of the legs. The cyclicstresses so set up in the head or upper end juncture of the legs'soreact on the upper end of the outside leg structure 100-103 thatsympathetic longitudinally elastic Vibrations, like those in the centralleg to which the vibrator is directly connected, are setup in theoutside leg structure, but at phase difference. The result is that boththe inside and outside leg structures undergo elastic elongation andcontraction, their joined upper end structures standing substantiallystationary, and their free lower bit-carrying ends reciprocating, themotions of the two leg structures being similar but at 180 phasedifference. Thus the bit element carried by the lower end of the outsideleg structure is descending, and vice versa.

u As stated earlier, the unitary head structure for the legs is a highimpedance region (stress anti-node, or velocity node), and is henceinherently substantially nonvibratory. The drill string, coupled to thishigh impedance point of thedrill, is inherently isolated from thevibration in the drill structure. In this fundamental and genericrespect, the quarter wave, fixed-free, drill of Figs. 8-15 is anacoustic analogue of the free-free drill of Fig. 4.

In a more specific: aspect, the drill configuration of Figs. 8-15 is'analogous also to the isolator configuration of Fig. 5. Viewing thedevice of Fig. 5 in this aspect, it canube seeny that the central leg 20and the concentric outside leg 45 comprise a unitary resonant circuit`strueture having a stationary node at the juncture with element 18'.Thisum'tary structure, viewed together with the oscillator and driverunit v14 for oscillatory drive purposes, and assuming the massiveenergy-storing vibratory collar 11 to be disconnected or omitted, wouldhave a characteristic resonant mode of operation exhibiting the abovementioned :stationary juncture point and also exhibiting out-of-phase,or opposed, vibration of the lower ends of legs 20 (with unit 14) andleg 45. It then becomes possible, I have found, to add, in place of theeliminated heavy collar 14, a very light andthin walled tubing whichbecomes a part of and vibrates in the resonant circuit comprising themembers 20', 45 and 14. The elimination of the large mass of collar 11causes the legs 20' and 45 to become a major or substantial portion ofthe resonant acoustic circuit structure, thus tuning out the mass of theoscillator and drive unit 14. The substituted light tubing becomes apart of the resonant circuit 20', 45 and 14, and vibrates as a part ofthis circuit without wastage of force. A

In Fig. 5a I have shown a modification of the lower portion of thesystem of Fig. v5, wherein a thin walled tubing 11a, such as referred toabove, has been substituted for the massive collar 11. Members 20' and45 are made fairly substantial, so as to handle substantial energy flowand storage in the system, and the substituted light tubing 11a thenneednot possess great energy storage capacity. In the illustrativeembodiment of Fig. 5a, the tubing 11a has a plain, flat end at thebottom,providing a thin annular edge in lieu of a drill bit. Thisconfiguration, I lhave found, will drill rapidly through the earth, andfunctions very well for taking cores at any chosen region. Moreover, bysimply giving such thin walled element 11a a greater diam-eter than anyother part of the drill, a continuous coring type of drilling operationcan be carried out.

A number of illustrative embodiments of the invention have now beendescribed and are illustrated in the drawings. It is to be understood,however, that these are but representative of various forms in which theinvention may be embodied in practice, and that various additionalspecific embodiments are Awithin the scope of the claims appendedhereto.

I claim:

l. An isolator adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratorysupport point characterized by low mechanical impedance, and asupporting means, comprising: an elongated longitudinally elasticallycompliant member of effectively substantially quarterwavelength for saidpredetermined frequency adapted to be coupled at one end to saidvibratory system at said vibratory support point, a massive inertiamember joined to the other end of said elongated member, and means forcoupling said massive inertia member to said supporting means.

2. An isolator adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratoryportion characterized by low mechanical impedance, and a supportingmeans, comprising: an elongated longitudinally elastically compliantmember of substantially half-wavelength for said predetermined frequencyadapted to be coupled at one end to said vibratory system at saidvibratory portion, and at its midpoint to said supporting means.

3. An isola-tor adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratorysupport point characterized by low mechanical impedance, and asupporting means, comprising: an elongated longitudinally elasticallycompliant member of substantially half-wavelength for said predeterminedfrequency adapted to be coupled at one end to said vibratory system atsaid vibratory support point, an elongated longitudinally elasticallycompliant member of substantially quarter-wavelength for said frequencyjoined at one end to the midpoint of said half-wavelength compliantmember, and a massive inertia member joined to the other end of saidelongated quarterwavelength compliant member, said massive inertiamember adapted for coupling to said support member.

4. An isolator adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratorysupport point characterized by low mechanical impedance, and asupporting means, comprising: a pair of parallel elongated elasticallycompliant members of quarter-wavelength for said frequency joined to oneanother at one end to form a unitary vibratory device, the opposite endof one of said elongated members being adapted for coupling to saidsupport point of said vibratory system, and means for coupling saidjoined ends of said elongated members to said support means.

5. The subject matter of claim 4, including also a massive inertia meanscoupled to said joined ends of said elongated members, and wherein saidmassive inertia member is interposed between said members and saidsupport means.

6. An isolator adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratorysupport point characterized by low mechanical impedance, and asupporting means, comprising: a helical spring adapted for coupling atits lower end to said vibratory system at said support point, and amassive inertia member coupled to the upper end of said helical springand to said support means.

7. An isolator adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratorysupport point characterized by low mechanical impedance, and asupporting means, comprising: a massive inertia means coupled to saidsupport means, a vertically elastically compliant coupling means ofeffectively quarter-wavelength comprised of a series of an odd number ofparallel, overlapped vertically extending and elongated elastic membersalternately connected, each to the next, at upper and lower endsthereof, said elastically compliant means being coupled at one end ofsaid series of members to the vibratory support point of said vibratingsystem, and at the other end of said series of members to said massiveinertia means.

8. An isolator adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratorysupport point characterized by low mechanical impedance, and asupporting means, comprising: an elongated longitudinally elasticallycompliant member of effectively substantially quarterwavelength for saidpredetermined frequency intercoupled between said support means and saidvibratory system at said vibratory support point, and means coupled tothe upper end portion of said elongated longitudinally elasticallycompliant member for resisting longitudinal vibratory movement of saidupper end portion of said member.

9. An isolator adapted for intercoupling between a vibratory drillsystem having a predetermined vibration frequency and having a vibratorysupport point characterized by low mechanical impedance, and asupporting means, comprising: a two-terminal device, including avibratory lower terminal joined to said vibratory support point of saidvibratory system, and a non-vibratory upper terminal, a massive inertiamember coupled to said upper terminal and to said support means, saiddevice having an elastically compliant portion which is elasticallyvibratory longitudinally of a direction line extending between saidupper and lower terminals, and which has mass and elasticity constants,establishing resonance thereof at said vibration frequency of saidvibratory system.

l0. ln a sonic well drilling system, the combination of: a sonic drillincluding a massive elastic drill rod with a bit on one end and amechanical vibrato-r attached thereto and arranged to exert vibratoryforces longitudinally of the rod at a frequency to generate alongitudinal standing wave in the rod, with a velocity antinode at theupper end thereof; a drill string for supporting said sonic drill; and aresonant vibration isolator intercoupled between said drill string andsaid sonic drill, said isolator embodying a two-terminal device,including a vibratory lower terminal joined to said sonic drill, and anon-vibratory upper terminal, a massive inertia member coupled to saidupper terminal and to said drill string, said device having anelastically compliant portion which is elastically vibratorylongitudinally of said drill string and sonic drill, and 'which has massand elasticity constants establishing resonance thereof at a standing-wave frequency generated in said drill rod by said vibrator.

l1. A wave transmission isolator adapted for interconnecting between asupporting means and a vibratory drill system having a predeterminedvibration frequency and direction and having a vibratory support point,comprising: an elastically resonant vibratory coupling structureincluding a vibratory portion of low acoustic impedance attached to saidsupport point of said drill system and having its direction of vibrationin the direction of vibration of said support point, and including alsoa non-vibratory portion of high acoustic impedance attached to saidsupporting means, said elastically vibratory coupling structure havingmass and elasticity constants establishing resonance thereof at thevibration frequency of said drill system.

l2. The subject matter of claim ll, wherein said portion of highacoustic impedance includes a massive inertia member.

13. The subject matter of claim 1l, wherein said coupling structureembodies two balanced oppositely phased elastically vibratory membersjoined at said non-vibratory portion thereof to provide said highimpedance.

14. A wave transmission isolator adapted for interconnecting between asupporting means and a vibratory drill system having a predeterminedvibration frequency and direction and having a vibratory support point,comprising: an elastically vibratory resonant coupling structure havingcoacting stiffness and vibrating mass for giving a resonant vibrationpattern at the vibration frequency of said drill, said couplingstructure being attached between said supporting means and said supportpoint of said drill, said coupling structure having its vibratory motionin the direction of said dr-ill vibration at said support point, and theresonant vibration pattern of said coupling structure having a highacoustic impedance at its point of attachment to said supporting meansand a low acoustic impedance at its point of attachment to saidvibratory support pp int- 15. The subject matter of claim 14, whereinsaid coupling structure includes a massive inertia member in the regionof its point of attachment to said supporting means to provide said highacoustic impedance.

16. The subject matter of claim 14, where said coupling structureembodies two balanced oppositely phased elastically vibratory membersjoined at said non-vibratory portion thereof to provide said highimpedance.

17. In a sonic well drilling system, the combination of a sonic drillincluding a massive freefree elastic rod with a bit on one end and amechanical vibrator attached thereto and being arranged to exertvibratory forces longitudinally of the rod at a frequency to generate alongitudinal standing wave in the rod, with a velocity antinode at theupper end thereof and a velocity node region at an intermediate regionthereof, a non-vibratory support attachment for said rod, and anisolator for isolating the standing wave vibration of said rod from saidnon-vibratory support attachment therefor, which isolator is 18intercoupled between said rod and said support attachment, said isolatorcomprising a jacket member connected at its upper end to said sup-portattachment and at its lower end to said velocity node region of saidrod, said jacket member surrounding said rod above said Velocity node.

18. The apparatus of claim 2 wherein said vibratory portion is asonically actuated bit characterized by said low mechanical impedance,wherein said vibration frequency is provided by a mechanical vibrator,and wherein said compliant member is a massive cross-section bar oflength corresponding to a standing wave pattern establishing saidhalf-wave length.

References Cited in the le of this patent UNITED STATES PATENTS HayesJuly 17, 1934

